Magnetic toner

Abstract

To provide a magnetic toner which is excellent in durability and developability even in the case of being applied to high-speed developing process or being used in a large-capacity process cartridge amount of toner in which is increased, and which has high degree of blackness. Provided is a magnetic toner having magnetic toner particles containing at least a binder resin and magnetic material particles each comprising a predetermined amount of a titanium compound, characterized in that:1) the magnetic material particles have a predetermined amount of adsorbed moisture at a relative vapor pressure of 50%; and2) a difference between the amount of moisture adsorbed to the magnetic material particles in an adsorbing process for increasing a relative vapor pressure and the amount of moisture adsorbed to the magnetic material particles in a desorbing process for reducing a relative vapor pressure is reduced.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to: an electrophotograph; an image forming method for visualizing an electrostatic image; and a magnetic toner for toner jetting.[0003]2. Description of the Related Art[0004]In recent years, an image forming apparatus has been further requested to have a high-speed process and long-term high reliability in addition to high definition, high appearance quality, and high image quality. A reduction of toner particle size and a sharpening of a toner particle size distribution have been attempted to achieve a high-resolution and high-definition development method. However, when the particle size of toner is merely reduced, dispersibility of a internal additive into a binder resin is apt to affect toner performance.[0005]In particular, in the case of magnetic toner having magnetic toner particles used for a one-component development method in which a reduction in size of an image forming apparatus...

AI Technical Summary

Benefits of technology

[0033]That is, an object of the present invention is to provide a magnetic toner which is excellent in durability and developability and has high degree of blackness, even when the magnetic toner is applied to high-speed developing process or used in a large-capacity process cartridge amount of toner in which is increased.

[0034]The inventors of the present invention have made extensive studies to find the following. That is, a magnetic toner having magnetic toner particles containing a binder resin and magnetic material particles each containing a titanium compound, in which: I) a ratio A [mass %] of a mass of moisture adsorbed to the magnetic material particles to a total mass of the magnetic material particles at a temperature of 28° C. and at a relative vapor pressure of 50% is 0.25 to 0.80 [mass %]; II) a difference at an arbitrary relative vapor pressure between a mass of moisture adsorbed to the magnetic material particles in an adsorbing process for increasing a relative vapor pressure at a constant temperature and a mass of moisture adsorbed to the magnetic material particles in a desorbing process for reducing a relative vapor pressure at the same temperature is 0.10 mass % or less based on the total mass of the magnetic material particles; and III) a ratio B [mass %] of a mass of the titanium compound in TiO2 equivalent to the total mass of the magnetic material particles is 0.1 to 10.0 [mass %], can achieve the object of the present invention. Thus, the inventors have completed the present invention.

[0035]According to the magnetic toner of the present invention, toner scattering around a letter image or the acceleration of fogging in the latter half of printing duration can be suppressed, even when the magnetic toner is applied to high-speed developing process or used in a large-capacity process cartridge amount of toner in which is increased.

[0036]According to the magnetic toner of the present invention, the occurrence of a flaw or filming on a photosensitive member can also be suppressed, even when a process speed is increased or when a contact charging method is adopted.

[0037]Furthermore, by using magnetic material particles in the present invention, even when a kneading step in the production process of magnetic toner is performed at a high temperature, magnetic toner having excellent blackness can be obtained.

Problems solved by technology

On the other hand, when the amount of magnetic material particles on the magnetic toner particle surface is excessively large, charge is apt to leak, so a high charge amount is hardly obtained.

As a result, a flaw on the photosensitive member is apt to develop, and the flaw may be responsible for an image defect.

As a result, a contamination of the photosensitive member such as filming is apt to occur.

However, when the magnetic toner having the external additive deteriorates owing to repetition of a printing step over a long period of time, the external additive is embedded into the magnetic toner particles, so influences of magnetic material particles exposed to magnetic toner particles surfaces become great.

Moreover, the progress of the selective development is apt to further accelerate various problems.

For example, the charging property of magnetic toner becomes susceptible to the environment.

In addition, the fluidity of the magnetic toner is reduced, so the toner is insufficiently supplied to a developing sleeve, and charge unevenness of a toner layer on the developing sleeve is caused.

If a toner has been insufficiently charged for the purpose of suppressing the scattering, the reduction of developability and the fogging may be caused.

However, the sharpening may be a factor for increasing toner production cost due to, for example, a reduction in yield.

There also arises a problem of declining degree of blackness in the case that the particle sizes of magnetic material particles are reduced.

However, the FeO (or Fe2+) content in the magnetic material particles reduces as deterioration with time due to oxidation proceeds, with the result that the degree of blackness of the magnetic material particles reduces.

Magnetic material particles with reduced particle sizes are susceptible to heat as well as time.

However, these magnetic material particles may cause defects concerning development.

For example, these magnetic material particles for uniformly being dispersed into magnetic toner particles are insufficient for the prevention of a reduction of blackness and an improvement of heat resistance.

However, when the above metals are merely added to the magnetic material particles, compatibility between a developability of the magnetic toner and an image quality and the like in a high-speed developing system are still susceptible to improvement.

The use of such magnetic material particles shows good developability at an initial stage of printing duration, however could not alleviate a reduction of image quality or developability such as the acceleration of fogging due to long-term use, particularly in a high-speed developing system.

However, the use of such magnetic material particles could not imparted sufficient charging stability to magnetic toner yet.

Furthermore, when the amount of an added element is excessively large or the smoothness of the surface of a magnetic material particle is not good, the amount of moisture adsorbed to the magnetic material particles becomes excessively large.

As a result, various problems arise from the fluidity or chargeability of magnetic toner such as a flaw or filming on a photosensitive member, fogging or fading of image, or scattering of the toner.

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